A separate filegroup for the indexes could be beneficial. I don't see any downside to it besides that you have to remember to create indexes on the correct filegroup.

>By default, all setups I have been done on several applications were putting all the indexes in their default settings. Thus, they were part of the MDF file. Recently, on a client's application as well as in here, we had the need to create combo indexes. So, while having created them, we assigned them in their own files. So, basically, they are located in an NDF file.
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>Now, considering the fact that whenever a recovery of a database is needed, I have everything needed in the application to recreate all the indexes, I found this approach to be quite nice. Basically, this allows the mdf to be smaller for every backup synchronizations I am doing. So, I am wondering, considering a 10 GB MDF file, which contains all the indexes which were created at first, would I be better to assign them in their own files. So, by doing that, the MDF will become smaller and I won't have to download them for every backup I am doing.
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>I expect the MDF to shrink to about 8 GB if I would separate the index from it.